The transient characteristics of GaN highly doped thin channel metal-semiconductor and metal-oxide-semiconductor field effect transistors were investigated by switching the transistors from the OFF to the ON state, Transient gated transmission line model Measurements showed that the channel resistance under the gate remains constant and the current collapse effects are linked to the transient variations of the series source-gate and gate-drain resistances. similar to what as previously reported for GaN/AlGaN heterostructure field effect transistors. The transient temperature measurements revealed that trapping processes responsible Cor the transient behavior cannot be described by the activation mechanism, (C) 2002 Published by Elsevier Science Ltd.